Ventilation controlling apparatus

ABSTRACT

Apparatus for controlling air moisture utilises a humidity sensor to produce an electrical signal indicative of air humidity. The signal provides input to a microprocessor which stores humidity values indicated by the signal and also uses the signal to compile a humidity reference base which may be derived from a time average of the relative humidity and, optionally, the current value thereof. The microprocessor further provides an output air moisture control signal when the sensed humidity exceeds the reference base by a predetermined amount.

This invention relates to apparatus for ventilating a building or a roomspace and to a humidity sensitive control device responding to Relative,Absolute or Specific humidity for such apparatus. The ventilatingapparatus can be a extractor fan, positive pressure fan, air heatrecovery using simultaneous intake and extract of air or any device ableto dry and or change the moisture content of the air and require controlbased on the water content in the air. The ventilation apparatus todisplace the existing air and thereby effect the water content bydilution of the air with the make up air.

It is the object of this invention to provide quantitative control of aventilation system based on assessment of the water content of air.

It is known to provide buildings, or rooms within buildings, withventilation apparatus including a humidity-sensitive control apparatus,arranged to activate the ventilation apparatus. Examples of mechanismavailable to determine this activation are as follows,

a) only when the interior humidity level is above a predeterminedthreshold (conventional humidistat)

b) detection of rate of change of increase in humidity (GB 2 133 588)

c) proportional extract ventilation rate in response to humidity levelabove a predetermined threshold (conventional variable speed fan withhumidity controller)

d) Detection of humidity with temperature change compensation(conventional humidistat technology in general use since 1983 —known asnight time set back).

e) Sampled, averaged and stored humidity level establishing apredetermined humidity threshold above this level (part of currentinvention).

All the above examples use the Relative Humidity (RH) scale to determinea level when to operate ventilation equipment. This is fraught withproblems arising from the RH scale itself which gives a value of watercontent (usually as a %) in relation to temperature, this giving anindicator of air saturation by moisture content. By way of examplecooking and tumble dryers produce copious amounts of water vapour,however a local %RH controller would only register a slight increase in%RH or in some cases a reduction of %RH, this is due to the simultaneousincrease in temperature causing the air to hold more moisture andtherefore not give cause to a rise in %RH. Other factors include changesin weather conditions causing fluctuations of ambient humidity andtemperature, and geographic locations such as near the sea, lakes,rivers and within valleys.

Controllers that monitor only current or memorise one off readings ofRelative Humidity such as GB 2 133 588 and GB 2 298 057 produce anomadic response, as at the moment of sensing a variety of influenceseffect these one off readings; Weather changes including pressure,temperature, and moisture content of air. Gradual changes of humidityand temperature. Fast short peaks of moisture (such as a kettle boilingbelow a sensor) or slow moisture production (such as clothes drying).

Controllers relying on the %RH scale require large tolerances in thesetting of the control levels due to the effects of changing temperatureand pressure. As the existing controllers are not relying on the watercontent increase of the air alone, erratic control results. The controlis not quantitative in relation to the water production to which it ismeant to control. The results to the user are irritating as they eitherhave equipment running too long too short or not at all, and apparentlynot duplicating previous control times.

Absolute and specific Humidity levels provide for true assessable levelsof the moisture content of air, a rise in moisture level would alwayscause a rise in absolute humidity and at a constant pressure, a rise ofspecific humidity.

A direct relation between Relative Humidity and Absolute Humidity can beachieved by not including the temperature aspect (measurement) when thesensor detects humidity or by way of the example compensating a RHsensor with a temperature sensor and calculating the Absolute Humidityin grams of water per meter cubed of air.

A further more accurate humidity assessment is achieved by using an airpressure sensor in conjunction with the Absolute Humidity levelproviding a Specific Humidity reading of grams of water per Kilogram ofair.

According to the invention a ventilation controlling apparatuscomprising a humidity sensor operable to produce an electrical signalthe level of which is determined by the humidity of air at the sensor,and microprocessor electrical circuitry coupled to the sensor, whereinsaid microprocessor stores the humidity, the average of the hunmidityreading is calculated over a period of time the value of which averageacts as a reference base of humidity, then when the measured humidityexceeds the reference base of humidity by a predetermined amount saidmicroprocessor means is arranged to provide a ventilation output controlsignal.

This invention is characterised by a ventilation controlling apparatuswhich has a variable reference point based on sampled humidity levelsand to a means of determining a reliable humidity reading to achieve thelength of period a ventilation apparatus should operate followingactivation. The sampled humidity levels being converted and stored asany of the following,

1. % Relative Humidity

2. Absolute Humidity

3. Specific Humidity

The processor operates the ventilator by relay when certain humidityconditions are met. Humidity readings are taken from continuous smallsampling periods the average of each sampling period is the basic inputfor all humidity readings stored in the memory of the microprocessor.The processor software calculates the humidity average value over afurther given period which providing a base reference, When the humidityincreases above a set threshold level above the base reference theventilation apparatus is activated. A second set of humidity readingsoccurs after activation of the ventilation apparatus. The humiditydifference from the base reference and the average of the second set ofhumidity reading provides the basis to calculate the total running timeof the ventilation apparatus. Subject to the humidity not returning tothe reference base level in which case the ventilator will bedeactivated.

Ventilation apparatus in accordance with the present invention ischaracterised by a ventilation controlling apparatus which has avariable reference point based on a set of sampled humidity levels suchan apparatus is more sensitive to humidity control requirements and ismore universally adaptable than apparatus relying solely on a humiditylevel or rate of change of humidity level. In its preferred form theapparatus can successfully discriminate from household humidityproduction and that from weather change, and temperature change, It isable to detect humidity produced slowly, i.e. that caused by clothesdrying and humidity produced in a large room, that is humidity levelsjust above ambient humidity.

The ambient humidity(Reference base) being defined by the controllerfrom an average of humidity samples taken by the controller over aperiod of time.

A second set of humidity readings(Relevant Humidity) are taken theaverage of which are compared with the reference base. The difference inthese readings provides a basis to calculate the ventilator runningtimes.

This Relevant Humidity value provides a level obtained when theventilation system (whatever its efficiency) is operating and when thehumidity source status is obtained, as such a humidity level taken atthis time has a direct relationship between the efficiency of theextraction source and the humidity producing source (although thissource can be variable). Determination of a ventilator control period atthe time of this second humidity reading provides a basis for theanticipated control period. The relevant humidity value is obtainedshortly after operation, typically three minutes, this is sufficientlyshort a period to discount ambient changes due to weather and geographicposition. At this time the vapour diffusion levels to cooler parts ofthe building are being contained as much as possible by the ventilatorunder control.

In its preferred form the apparatus can successfully determine controlperiods and thereby optimise the ventilation unit for efficiency andcondensation control.

A ventilation control apparatus including a control unit and ventilatorin accordance with the present invention, will now be described, by wayof example, with reference to the accompanying drawings, in which:

FIG. 1 shows the system schematically;

FIG. 2 shows the system schematically for specific humidity;

FIG. 3 illustrates the relationship between % Relative Humidity—AbsoluteHumidity and Temperature

The ventilation controlling apparatus comprises an extractor fan [1]mounted in an external wall or window of a conventional domesticdwelling, close to the moisture sources in either the kitchen orbathroom. The extractor fan [1] is electrically powered and connected bywire to the output relay [9] of the control unit [11]. The control unit[11]includes a microprocessor [6], probe sense amplifier [3], probe logconverter [4], analogue to digital converter [5], Relay [9] and LEDstatus indicator [8], and is connected to thermistor [7] and humiditysensor [2].

The sensed Humidity is continually supplied to the microprocessor viaprobe sense amplifier [3], the probe log converter [4] and A to Dconverter [5]. The microprocessor programming converts the Humidityreadings to Absolute humidity with as required the temperature inputfrom the thermistor, readings from the humidity sensor are averaged over30 seconds this average value is then supplied for memory storage, thesereadings are then stored for two hours the average over this two hourperiod is used as the base reference. The base reference is updatedevery two hours with the average of the absolute humidity reading takenover the preceding two hour period. During activation periods of theextractor fan humidity readings for the base reference are suspended,this is to avoid spurious ambient readings during the desiccationperiod.

A threshold level of absolute humidity above the base reference ischosen sufficiently high to avoid ambient humidity variations that couldoccur over a two hour period but low enough to activate the ventilatorwith moisture production. The Absolute Humidity threshold level isaltered at different temperatures, as shown in Table 1 below.

Once the Absolute humidity has gone above the threshold the ventilatoris activated, after three minutes of activation the Absolute Humiditylevel is again compared with the base reference level, the level ofAbsolute humidity above this base will determine the total running timeas shown in Table 2 below.

Note the controller can be set to operate for double the periodexpressed in Table 2 when used with less efficient ventilation systemssuch as air heat recovery and positive air pressure systems. This isachieved by cutting link [12] which adjusts the microprocessor program.

If at any time during ventilator activation the absolute humidity levelfalls to the same or less than the base reference level then theactivation period is suspended.

If at the end of a time activation period the Absolute Humidity is abovethe Threshold level then a further activation is activated as shown inTable 2.

Specific Humidity Controller as FIG. 2, Operation as Absolute HumidityController with Pressure input compensating for atmospheric changes ofpressure.

Relative Humidity as FIG. 1, Operation as Absolute Humidity Controllerwithout thermister input. With the following control; The %RH is storedover the two hour period and used as the base reference (being updatedevery two hours). The base reference is compared with humidity samplestaken after 3 minutes of ventilator operation (this sample taken over 30seconds and then averaged). The difference %RH between the base averageand the sample after 3 minutes is used to calculate total running, time.

For general extraction this would equate to 2×% Relative Humidity(%RH)difference =number of minutes the extractor operates For ventilationunits such as positive pressure or air heat recovery the minimumoperation periods would be double, i.e. 4×% Relative Humidity difference=number of minutes of ventilation.

TABLE 1 RUNNING TIME CALCULATION BASED ON ABSOLUTE HUMIDITY LEVEL 3MINUTES AFTER VENTILATOR OPERATION = C × D Threshold level Level aboveTemperature above ref.: threshold Multiplication Range ° C. B C numberRunning time A g/M3 of H2O in air g/M3 of H2O in air D Minutes 0-5 0.1030.00 C × D  5-10 0.20 20.00 C × D 10-15 0.30 10.00 C × D 15-20 0.407.50 C × D 20-25 0.50 6.00 C × D 25-30 0.60 5.00 C × D 30-35 0.80 4.00 C× D 35> 1.00 3.00 C × D

TABLE 2 TEMPERATURE VS ABSOLUTE HUMIDITY THRESHOLD CONTROL ABOVE BASEREFERENCE OF ABSOLUTE HUMIDITY Water Multiplication Set level aboveTemperature Content No. ref: Range ° C. B C D A g/M3 of H2O X g/M3 ofH2O in air 0-5 0.05 1 0.10  5-10 0.05 2 0.20 10-15 0.05 3 0.30 15-200.05 4 0.40 20-25 0.05 5 0.50 25-30 0.05 6 0.60 30-35 0.05 8 0.80 35>0.05 10 1.00 A = Temperature range B = Absolute Humidity threshold level

KEY FOR FIG. 1

A control for ventilation apparatus 1, humidity sensor 2 the output ofwhich are amplified by probe sense amplifier 3 this output is suppliedto probe log converter 4 which is then supplied to the Analogue toDigital converter 5 this digital information then supplied to themicroprocessor 6. Thermistor 7 connected to microprocessor 6.

The processor operates the ventilator by relay 9 when certain absolutehumidity condition are met. The processor calculates the absolutehumidity the average value over a given period is used as a reference,when the absolute value of humidity increases above a given thresholdabove this reference ventilation apparatus 1 is activated. A furtherhumidity reading after a given time is taken while the ventilationapparatus 1 has been activated, the humidity difference from thereference and this further reading provides the basis to calculate theactual total running time of the ventilation apparatus 1.

KEY FOR FIG. 2

A control for ventilation apparatus 1, humidity sensor 2 the output ofwhich are amplified by probe sense amplifier 3 this output is suppliedto probe log converter 4 which is then supplied to the Analogue toDigital converter 5 this digital information then supplied to themicroprocessor 6. Thermistor 7 and pressure transducer 10 are connectedto microprocessor 6.

The processor operates the ventilator by relay 9 when certain specifichumidity condition are met. The processor calculates the specifichumidity the average value over a given period is used as a reference,when the absolute value of humidity increases above a given thresholdabove this reference ventilation apparatus 1 is activated. A furtherhumidity reading after a given time is taken while the ventilationapparatus 1 has been activated, the humidity difference from thereference and this further reading provides the basis to calculate theactual total running time of the ventilation apparatus 1.

What is claimed is:
 1. Air moisture controlling apparatus comprising ahumidity sensor operable to produce an electrical signal the level ofwhich is determined by the humidity of air at the sensor, andmicroprocessor means coupled to the sensor whereby to receive saidsignal, in which the microprocessor means is arranged to provide anoutput air moisture control signal when the measured humidity exceeds areference base of humidity by a predetermined amount; wherein themicroprocessor stores humidity values indicated by the sensor signal,calculates an average value over a time period, and uses the calculatedaverage as the said reference base of humidity.
 2. Air moisturecontrolling apparatus according to claim 1, wherein the microprocessormeans compares a second humidity reading, taken after a significantperiod following provision of said air moisture output control signal,with the reference base of humidity, and the difference in humiditylevels provides a calculation basis for the duration of the air moistureoutput control signal.
 3. Air moisture controlling apparatus accordingto claim 2, wherein the second humidity reading is taken in a smallsampling period after the said significant period following provision ofthe air moisture output control signal.
 4. Air moisture controllingapparatus according to claim 1, wherein said microprocessor means storesand averages the humidity in small sampling periods, compiles theaverage of the humidity readings in these small sampling periods over alonger time period the average of which acts as a reference base ofhumidity, and when the average value of humidity in the current smallsampling period exceeds the reference base of humidity by apredetermined threshold said microprocessor means is arranged to providesaid air moisture output control signal.
 5. Air moisture controllingapparatus according to claim 1, wherein the output air moisture controlsignal is adapted to deactivate air moisture control if the measuredhumidity decreases to the reference base of humidity.
 6. Air moisturecontrolling apparatus according to claim 1, wherein said microprocessormeans is arranged to detect store and calculate based on the AbsoluteHumidity, the humidity readings from the humidity sensor being adjustedas required by readings from a temperature sensor to match thecharacteristics of the humidity sensor used.
 7. Air moisture controllingapparatus according to claim 1, wherein said microprocessor means isarranged to detect store and calculate based on the percent RelativeHumidity, the humidity readings from the humidity sensor being adjustedas required by readings from a temperature sensor to match thecharacteristics of the humidity sensor used.
 8. Air moisture controllingapparatus according to claim 1, wherein said microprocessor means isarranged to detect store and calculate based on the Specific Humidity,the humidity readings from the humidity sensor being adjusted asrequired by readings from a temperature sensor and from an air pressuresensor to match the characteristics of the humidity sensor used.
 9. Airmoisture controlling apparatus according to claim 1, wherein the outputcontrol signal is supplied to ventilating apparatus.
 10. Apparatus forchanging the moisture content of air in a building or room space, havingcontrol means comprising air moisture controlling apparatus according toclaim
 1. 11. Air moisture controlling apparatus comprising a humiditysensor operable to produce an electrical signal the level of which isdetermined by the humidity of air at the sensor, and microprocessormeans coupled to the sensor whereby to receive said signal, in which themicroprocessor means is arranged to provide an output air moisturecontrol signal when the measured humidity exceeds a reference base ofhumidity by a predetermined amount; wherein the microprocessor storeshumidity values indicated by the sensor signal, and derives the saidreference base of humidity from the stored humidity values.
 12. Airmoisture controlling apparatus according to claim 1, wherein thehumidity reference base is compiled by the microprocessor from both theaveraged stored reference value of relative humidity and the currentlysensed value of relative humidity.